Abstract: A flexible boot having a bellows and mount portions on both axial ends of the bellows portion at which the boot is mounted on parts of a mechanism such as an automotive constant velocity joint. The flexible boot has an anti-degradation agent make-up element made of a material which contains an anti-degradation agent and which is capable of allowing the anti-degradation agent to precipitate on the surface thereof. The anti-degradation agent make-up element is fitted on at least a portion of the outer surface of the bellows so that the anti-degradation agent precipitated on the surface of the material of the anti-degradation agent make-up element is caused to progressively immigrate into the material of the bellows thereby making-up the anti-degradation agent in the bellows.